Generally, a passenger detection device is used for providing information of passengers on seats of a vehicle. Referring to JP-2003-14528-A, for example, the passenger detection device includes multiple load sensors and a passenger detection electronic control unit (ECU), in which at least one passenger detection threshold value is memorized. Based on the passenger detection threshold value, the passenger information can be determined.
Specifically, by comparing a total of detection data of the multiple load sensors with the two passenger detection threshold values, it is determined whether or not the seat is vacant, or whether or not the passenger on the seat is analdlult. When the total is smaller than the passenger detection threshold value for a child-vacancy judgment, the passenger detection ECU determines that the seat is vacant. On the other hand, when the total is larger than or equal to the passenger detection threshold value for the child-vacancy judgment, and smaller than the passenger detection threshold value for a child-adult judgment, the passenger detection ECU determines that the passenger is a child. When the total is larger than or equal to the passenger detection threshold value for the child-adult judgment, the passenger detection ECU determines that the passenger is an adult. In the case where the seat is vacant or the passenger is a child, an airbag corresponding to this seat will be restricted from deploying. In contrast, when the passenger is an adult, the airbag can be activated. Furthermore, when the passenger having been determined to be an adult does not wear a seatbelt, a seatbelt-wear alarm is given.
However, a vacancy zero point (detection load for vacant seat) of the load sensor is readily influenced by errors of both an attachment of the load sensor to the seat and an attachment of the seat, at which the load sensors having been mounted, to the vehicle. Therefore, there is a variation in the vacancy zero points of the multiple load sensors mounted at the seat.
FIG. 8A shows the variation in the vacancy zero points of the load sensors a1-d1. The load sensors a1 and b1 are mounted at the two front corners of the seat, and the load sensors c1 and d1 are mounted at the two rear corners of the seat. Here, a sensor detection range is an inherent dynamic range of the load sensor. A zero-point variation range is a range of the vacancy zero points which is admissible to be input to a passenger detection ECU considering the variation in the vacancy zero points. In FIG. 8A, (+) indicates a plus direction (downward direction) of the load, and (−) indicates a minus direction of the load (upward direction). Referring to FIG. 8A, the vacancy zero points of the four load sensors a1-b1 are dispersed at the plus side and the minus side.
When a passenger sits on the seat, a1-d1 ownward load is additionally exerted on the seat, so that each of the load sensors a1-d1 has a plus-side detection load in addition to the vacancy zero point thereof, as shown in FIG. 8B.
When the vehicle is accelerated or decelerated, the load exerted on the seat will be changed. FIG. 8C shows the detection loads of the load sensors a1-d1 when the vehicle is accelerated. As compared with FIG. 8B, the detection loads of the load sensors a1, b1, c1, d1 indicted in FIG. 8C are respectively moved toward the minus side by Δfa, the minus side by Δfb, the plus side by ΔFc and the plus side by ΔFd.
Because the vacancy zero points of the load sensors a1 and b1 are originally near a lower limit of the vacancy zero point variation range, the detection loads of the load sensor a1 and b1 exceed a lower limit of the sensor detection range. As shown in FIG. 8C, the exceeding parts of the detection loads are eliminated, so that the detection loads are limited within the sensor detection range. Therefore, the real load exerted on the seat cannot be detected by the load sensors a1-d1. Specifically, as compared with FIG. 8B, the detection load of the load sensor a1 has a minus-side movement value Δfa, while the real minus-side movement value is (Δfa+Δfa′). Similarly, the detection load of the load sensor b1 has a minus-side movement value Δfb, while the real minus-side movement value is (Δfb+Δfb′). On the other hand, the detection loads of the load sensors c1 and d1 does not exceed the sensor detection range to be the loads exerted on the corresponding portions of the seat. Therefore, an actual total of the detection loads of the load sensors a1-d1 is (Δfc+Δfd−Δfa−Δfb), instead of the real total (Δfc+Δfd−Δfa−Δfb−Δfa′−Δfb′). That is, (−Δfa′−Δfb′) is not added to the actual total, so that the actual total of the detection loads of the load sensors a1-d1 is larger than the load exerted on the seat.
Therefore, the actual total of the detection loads is changed from the minus side toward the plus side. If the total exceeds the passenger judgment threshold value, a judgment result of the passenger information, which is determined by the passenger detection ECU before the vehicle is accelerated, will be switched from “child” to “adult” even when the passenger is actually a child.
When the vehicle is turned while being accelerated, a load in the plus side will be centralized at one of the four load sensors. FIG. 9A shows loads detected in an ordinary traveling of the vehicle. FIG. 9B shows loads detected when the vehicle is turned while being accelerated. Here, the load beyond the upper limit of the sensor detection range is centralized at the load sensor d1 among the load sensors c1 and d1 which are mounted at the vehicle rear portion. In this case, the exceeding part Δfd′ at the plus side is eliminated from the detection load, so that the detection load of the load sensor d1 is limited within the sensor detection range. Thus, the total of the detection loads of the load sensors a1-d1 will be smaller than the load exerted on the seat.
Therefore, the total of the detection loads of the load sensors a1-d1 is changed from the plus side toward the minus side. If the total exceeds the passenger judgment threshold value, the judgment result of the passenger information, which is determined by the passenger detection ECU before the vehicle is turned, will be switched from “adult” to “child” or “vacancy” even when the passenger is actually an adult.